2

Challenges and Opportunities Associated with Conversion

Session 2 of the symposium (see Appendix A) focused on technical challenges associated with conversion and potential solutions for overcoming those challenges. Three panels of Russian Federation (R.F.) and U.S. speakers were organized to address these topics:

•  Panel 2.1: Technical challenges associated with conversion and potential solutions featured Russian and U.S. presentations on low enriched uranium (LEU) fuel design, core modifications, and approaches for maintaining reactor performance and missions after conversion.

•  Panel 2.2: Other technical challenges associated with conversion featured presentations on ageing and obsolescence, regulatory challenges, and challenges posed by research reactors that cannot be converted.

•  Panel 2.3: How challenges associated with previously converted reactors were overcome featured presentations on approaches for overcoming the conversion challenges identified by the other panels in this session.

These panel presentations are summarized in this chapter along with key thoughts from the participant discussions.

FUEL DESIGN FOR CONVERSION

Two presentations on fuel design for conversion were given by Panel 2.1 speakers: Daniel Wachs (Idaho National Laboratory) reported on efforts to develop LEU fuels for converting U.S.-origin reactors (Wachs, 2011),



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2 Challenges and Opportunities Associated with Conversion S ession 2 of the symposium (see Appendix A) focused on technical chal- lenges associated with conversion and potential solutions for overcom- ing those challenges. Three panels of Russian Federation (R.F.) and U.S. speakers were organized to address these topics: • Panel 2.1: Technical challenges associated with conversion and potential solutions featured Russian and U.S. presentations on low enriched uranium (LEU) fuel design, core modifications, and approaches for main- taining reactor performance and missions after conversion. • Panel 2.2: Other technical challenges associated with conversion featured presentations on ageing and obsolescence, regulatory challenges, and challenges posed by research reactors that cannot be converted. • Panel 2.3: How challenges associated with previously converted reactors were overcome featured presentations on approaches for overcom- ing the conversion challenges identified by the other panels in this session. These panel presentations are summarized in this chapter along with key thoughts from the participant discussions. FUEL DESIGN FOR CONVERSION Two presentations on fuel design for conversion were given by Panel 2.1 speakers: Daniel Wachs (Idaho National Laboratory) reported on efforts to develop LEU fuels for converting U.S.-origin reactors (Wachs, 2011), 21

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22 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS and Yu.S. Cherepnin (Dollezhal Scientific Research and Design Institute of Energy Technologies [NIKIET]) described progress and prospects for reduction of fuel enrichment in Russian-origin reactors (Cherepnin, 2011). Fuel Design for U.S.-Origin Reactors Daniel Wachs Highly enriched uranium (HEU) fuel elements in U.S.-origin research and test reactors consist of aluminum-clad plates (see Chapter 1) that contain a UAlx or U3O8-aluminum dispersion fuel meat clad in aluminum or a uranium-zirconium hydride (UZrHx) fuel meat clad in stainless steel (TRIGA fuel). Work carried out by Argonne National Laboratory and the Idaho National Laboratory, in cooperation with other American, European, and Korean organizations, has resulted in the development of three LEU dispersion fuel systems1 for conversion of plate-type reactors: UAlx (density = 2.3 grams of uranium per cubic centimeter [gU/cm3]) • U3O8 (3.2 gU/cm3) • U3Si2 (4.8 gU/cm3) • These fuel systems are adequate for converting all but “high per- formance” research and test reactors.2 There are six HEU-fueled high- performance research reactors in the United States3 as well as four HEU-fueled high-performance research reactors in Europe that cannot be 1 The Reduced Enrichment for Research and Test Reactors (RERTR) program (see Chapter 1) also participated in the qualification of a fourth LEU fuel system: a uranium-zirconium hydride with an erbium burnable poison (UZrHx-Er) fuel system that is used for the conversion of TRIGA (Test, Research, Isotope production—General Atomics) reactors. General Atomics began developing a higher-density fuel (up to 3.7 gU/cm3) before the RERTR program was started in 1978. The RERTR program performed irradiation tests on 20/20 (i.e., 20 weight percent uranium, 20 percent enriched), 30/20, and 45/20 fuels. The 30/20 fuel was used to convert the Oregon State TRIGA Mark II reactor, discussed later in this chapter, and the University of Wisconsin Nuclear Reactor, discussed in Chapter 3, as well as a number of other TRIGA reactors in the United States and abroad. 2 These high-performance reactors have high-power-density (i.e., high-flux-density) cores. Fuels having higher uranium densities than are available with existing LEU fuels are required to convert these reactors. 3 As noted in Chapter 1, there are two additional HEU-fueled research reactors in the United States (NTR General Electric and TREAT; see Footnote 20 in Chapter 1) that appear to be convertible using current-type LEU fuels. The Department of Energy (DOE) is com- pleting studies to confirm the feasibility of converting these reactors using current-type LEU fuels. Additional research will be required to more fully develop the capability to fabricate these LEU fuels.

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23 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION converted with these existing LEU fuel systems. The U.S. reactors are shown in Table 1-1 in Chapter 1; the European reactors are the following: • Belgian Reactor 2 (BR2) at the Belgian Nuclear Research Centre in Mol, Belgium • Forschungsreaktor München II (FRM-II) at the Technical Univer- sity of Munich, Germany • Jules Horowitz Reactor (JHR), under construction at the CEA Cadarache Research Centre in Cadarache, France (discussed in Chapter 4) • Réacteur à Haut Flux (RHF) at the Institut Max von Laue-Paul Langevin (ILL) in Grenoble, France Higher-density LEU fuel systems based on uranium-molybdenum (UMo) alloys are now under development for use in converting these U.S. and European reactors. Test irradiations have been carried out on several UMo alloys to assess their suitability for use as fuel for these reactors. Testing revealed that alloy phases with high U/Mo ratios (e.g., U-10Mo4) were most stable under irradiation because they suppressed the formation of fission gas bubbles.5 Two LEU fuel systems based on this alloy are now under development by Idaho National Laboratory and partners: • UMo dispersion fuel: A UMo alloy dispersed in an aluminum ma- trix with uranium densities up to 8.5 gU/cm3. An LEU fuel system based on this material is being developed for conversion of BR2, RHF, and JHR.6 • Monolithic UMo fuel: Metallic UMo foils with a uranium density of 15.5 gU/cm3. An LEU fuel system based on this material is being devel- oped for conversion of ATR, HFIR, NBSR, MITR, and MURR (Figure 2-1). Test irradiations of fuel elements containing both of these materials are now being carried out to develop and qualify these fuel systems. UMo Dispersion LEU Fuel Initial irradiations of fuel elements containing UMo dispersions re- sulted in the formation of interaction layers between the UMo and Al particles and the development of porosity and distortion (pillowing). The addition of small amounts (~2 percent) silicon to the aluminum phase was 4 That is, alloys consisting of 9 parts uranium to 1 part molybdenum by weight. 5 Fission gas bubbles are formed in the fuel phase as a result of the production of gaseous fission products. 6 At present, no LEU replacement fuel has been identified for the FRM II reactor.

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24 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS FIGURE 2-1 Schematic cross-section of a research reactor fuel element containing monolithic UMo. SOURCE: Wachs (2011). Figure 2-1.eps bitmap found to suppress the development of this interaction layer at burnups of up to 70 percent. However, test irradiations of this fuel material at high power (~ 500 watts per square centimeter [W/cm2]), high uranium loadings (> 8 gU/cm3), and high burnup (> 70 percent) resulted in the formation of small blisters on the fuel plates. Follow-up experiments are planned for the fall of 2011 to determine why such blistering occurs and how the fuel ele- ment can be modified to eliminate it. A bounding-case irradiation of this fuel material in BR2 is planned for 2011-2012. UMo Monolithic LEU Fuel Fuel plates under development for high-performance U.S. reactors con- sist of a UMo alloy foil (“U-10Mo Foil” in Figure 2-1) surrounded by a zirconium fission recoil barrier (“2X Zirconium Interlayer” in Figure 2-1) in an aluminum cladding (“Al 6061 Cladding” in Figure 2-1). The barrier is intended to prevent interactions at the interface of the fuel meat and cladding. A key issue for this fuel is the stability of this interface. Although the interface is mechanically stable, swelling of the fuel meat during irradia- tion could lead to the development of porosity at the interface and eventual delamination of the foil from the cladding. Such swelling and delamination could prove to be a life-limiting factor for this fuel system. Qualification testing of this fuel for three high-performance research reactors (MITR, MURR, and NBSR) is currently under way. A partial fuel assembly7 is currently being irradiated in ATR at the Idaho National Laboratory (Figure 2-2), and irradiation of ATR fuel elements is planned 7As the name suggests, a partial fuel assembly contains only portions of a full fuel assembly. For example, a partial assembly might contain fewer fuel plates than a full assembly.

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25 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION FIGURE 2.2 End view of a partial fuel 2-2.eps(AIFP-7) containing monolithic Figure assembly UMo fuel that is currently undergoing test irradiations in the ATR. SOURCE: bitmap Wachs (2011). to begin in 2012. Lead test assembly irradiations are planned once these irradiations are completed. Testing of this fuel system for use in the highest-performance U.S. reactors (i.e., ATR, HFIR) is planned to begin in late 2011. Bounding- condition irradiation tests (greater than 500 W/cm2 and greater than 60 percent burnup) on a full-size fuel plate will be carried out at the ATR in late 2011. Fuel qualification testing will be initiated after these irradiation tests are completed. Fuel Design for Russian-Origin Reactors Yu.S. Cherepnin Most Russian research and test reactors use HEU fuels consisting of UO2-aluminum dispersions fabricated as thin-walled tubular elements of various enrichments and configurations. A Russian program was started in the 1990s to further reduce the enrichment of fuel used in Russian-origin research reactors that are located outside of the Russian Federation. This work has been led by three Russian organizations (NIKIET, Bochvar All-

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26 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS Russian Scientific Research Institute for Inorganic Materials [VNIINM], and Novosibirsk Chemical Concentrates Plant [NZKhK]) with the collabo- ration of several other organizations and customers (i.e., research reactor operators) and has resulted in the development of LEU fuels. The initial phase of this program created UO2-Al LEU fuel assem- blies for conversion of all existing Russian-origin research reactors that are located outside of the Russian Federation. The aim was to reduce the enrichment of uranium in the fuel elements without changing fuel element geometry. LEU fuel assemblies of several designs have been developed (Figure 2-3): • VVR-M2 fuel assembly. This assembly has a tubular geometry and contains a UO2-aluminum dispersion fuel meat with a density of 2.5 gU/cm3. These fuel assemblies have undergone a full cycle of design, testing, and licensing and are currently being manufactured at the fuel production facility at NZKhK in Novosibirsk. This fuel is being supplied to Russian- origin research reactors in Hungary, Vietnam, and Romania. • IRT-4M fuel assembly. This assembly has a square geometry and contains a UO2-aluminum dispersion fuel meat with a density of 3.0 gU/cm3. This fuel, which is fully licensed, is the highest-demand fuel for Russian-origin research reactors located outside of the Russian Federation. This fuel is being supplied to Russian-origin research reactors in the Czech Republic, Uzbekistan, and Libya. • VVR-KN fuel assembly. This assembly has a hexagonal geometry and is being developed for use in a Russian-origin research reactor in Ka- zakhstan. It will replace a 36 percent enriched assembly that is now in use. Three assemblies have been manufactured and are now being irradiated in the reactor. Conversion studies and fuel qualification activities for this reac - tor are proceeding in close cooperation with the reactor operator, producing good results. • MR fuel assembly. Design work is about to begin to develop a UO2-aluminum dispersion fuel for this tubular fuel assembly. The fuel meat (which currently has an enrichment of 36 percent) is expected to have an enrichment of 19.5 percent with a density no less than 3.5 g U/cm3. It is expected to take about a year to complete this design work and manufac- ture fuel assemblies for testing. The 19.5 percent enriched fuel will be used in the Russian-origin MARIA research reactor in Poland. The transition to these LEU fuel assemblies has proceeded using the same fabrication technologies and equipment for producing HEU fuel. However, the use of LEU fuels can reduce reactor “performance” (i.e., re- duce neutron flux densities in the core and reflector regions) by up to about 15 percent and shorten fuel replacement cycles. Consequently, the develop-

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FIGURE 2-3 Schematic illustrations of (left) VVR-M2 tubular fuel assembly, (middle) IRT-4M square fuel assembly, and (right) MR tubular fuel assembly. The VVR-KN hexagonal fuel assembly is not shown. SOURCE: Cherepnin (2011). 27

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28 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS ment of higher-density LEU fuels is needed to maintain reactor performance and fuel cycle length and also to increase fuel robustness by allowing an increase in cladding thickness. The development of higher-density fuels is being carried out in a second phase of the Russian program to reduce fuel enrichments. Work is proceed- ing on a UMo dispersion LEU fuel with a density of about 5 gU/cm3.8 Test irradiations of this material have been carried out to burnups of 40-60 percent. Design efforts are under way for two fuel assembly types: IRT-3M (which has a tubular geometry) and IRT-U (which has a pin geometry). The third phase of the reduced enrichment program is envisaged to involve the development of completely new fuel designs for future reac- tors. These new designs should be safe, reliable, easy to fabricate, and economically efficient compared to current designs. UMo monolithic LEU fuels manufactured in the form of pins appear to be a promising future de- sign concept. These could be arranged in geometries to mimic the tubular, square, and hexagonal geometries of current-generation fuel assemblies that are used in Russian-origin research reactors. CORE MODIFICATIONS FOR CONVERSION Two presentations on modifications of research reactor cores to address the technical challenges of conversion were given by Panel 2.1 speakers: John Stevens (Argonne National Laboratory) provided a U.S. viewpoint on core modifications (Stevens, 2011), and I.T. Tetiyakov (NIKIET) provided a Russian viewpoint (Tetiyakov, 2011). U.S. Viewpoint on Core Modifications John Stevens The conversion of a research reactor from HEU to LEU fuel can result in performance penalties in the reactor, primarily arising from the reduced density of uranium-235 and absorption of neutrons by uranium-238. Modi- fications to a reactor core may be required to overcome these penalties. Several core modification strategies have been used to overcome the penal- ties associated with the conversion of U.S.-origin research reactors; these include modifications to the following: 8 Extrusion processes are used to manufacture research reactor fuel in Russia, whereas rolling processes are used to produce research reactor fuels in the United States and Europe. Both processes produce suitable fuels, but fuel produced by extrusion generally has a lower density than fuel produced by rolling.

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29 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION • fuel plate thickness and reflector locations; • fuel meat thickness; • uranium and burnable absorber loading; and • fueled height of the core. When making modifications to a reactor core one should strive to change as little as possible. Two particularly successful strategies for over- coming performance penalties that entail minimal changes are (1) tuning the burnable absorber to match the fuel composition; and (2) if cost is ac- ceptable, modifying reflector materials and/or geometries. Of course, the fuel will, by definition, change from HEU to LEU during the conversion process, and the LEU fuel must be “acceptable” for conver- sion. An LEU fuel is considered to be acceptable for conversion when it meets the following criteria: • Qualified: the fuel assembly has been successfully irradiation tested and is licensable. • Commercially available: The fuel assembly is available from a com- mercial manufacturer. • Suitable: The fuel assembly satisfies the criteria for LEU conver- sion of a specific reactor; safety criteria are satisfied; fuel service lifetime is comparable to current HEU fuel; and the performance of experiments is not significantly lower than for HEU fuel. • The reactor operator and regulator agree to accept fuel assembly for conversion. Successful conversion requires the involvement of reactor operators to un- derstand their needs and constraints. The following examples were presented to illustrate some of the core modification options that are available to overcome conversion penalties. Some of the reactors described in these examples have already been con- verted, whereas others have not yet been converted. Oregon State TRIGA Mark II Reactor The Oregon State TRIGA reactor is licensed to operate at a steady state power of 1.1 megawatts (MW) and can pulse to 2,500 MW with a peak steady-state thermal flux of about 1013 neutrons per square centimeter per second (n/cm2-s) in the B1 position. The reactor was originally fueled with a 70 percent enriched UZrHx fuel with a 1.6 weight percent erbium burnable absorber. The reactor was converted to a 19.75 percent enriched UZrHx fuel with a 1.1 weight percent erbium burnable absorber.

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30 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS Depletion at 1 MW, Hot Conditions, All Rods Out (Fuel 327C, Coolant 50C) HEU FLIP Fuel (82+3) LEU 1.1% Er Fuel (86+3) 6.00 LEU 0.9% Er Fuel (74+3) 5.00 (biased 0.48%dk/k per HEU Measurement) 4.00 Excess Reactivity (%dk/k) 3.00 2.00 1.00 0.00 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 -1.00 Years at 50 MWd/yr FIGURE 2-4 Plot of excess reactivity versus time at constant burnup rate for the Oregon State TRIGA Reactor. Adjusting the burnable poison to 1.1 percent in the Figure 2-4.eps LEU core provided an acceptable shutdown margin and maintained the longevity of the core (middle curve in the figure). SOURCE: Stevens (2011). This reactor has a lifetime core, and it was important to the reactor operator to maintain a full grid of fuel assemblies in the converted core to maintain flexibility for conducting irradiation experiments. However, maintaining a full core reduced the shutdown margin (i.e., raised the excess reactivity) at the beginning of life of the new reactor core. Adjusting the erbium burnable poison to 1.1 percent in the converted core restored the shutdown margin and maintained the longevity of the core (Figure 2-4). RPI Research Reactor The RPI research reactor is licensed to operate at 1 MW power and has a peak flux of about 3.1 × 1013 n/cm2-s. The core was converted from a 93 percent enriched UAlx-aluminum dispersion fuel to 19.75 percent enriched uranium silicide (U3Si2)-aluminum dispersion fuel in 2007. The LEU fuel contains slightly more uranium-235 than the HEU fuel it replaced to ac- count for the increased neutron absorption by uranium-238.

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31 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION The conversion goal for this reactor was to allow for 10 years of op- eration at acceptable neutron flux density levels using the same number or fewer fuel assemblies. A silicide fuel with the same fuel meat thickness as the original HEU fuel met this goal when the core contained 17 fuel assemblies. However, by increasing the thickness of the fuel meat by 0.1 millimeters, the conversion goal could be met using only 13 fuel assemblies, a savings of 4 assemblies. Additionally, by changing the locations of some of the beryllium reflector blocks, designers were able to increase neutron flux densities in key locations in the reactor core to better suit experimental needs. MURR MURR is a high-performance research reactor with a very compact core (core volume of only 33 liters with 4.3 liters of fuel meat) with a peak thermal flux of about 6.0 × 1014 n/cm2-s (Figure 2-5). The reactor is FIGURE 2-5 Photo of the MURR reactor core. SOURCE: Roglans (2011). Figure 2-5.eps bitmap

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50 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS issues that are impacted by conversion to LEU. Specific areas of focus in the application include the following: • Reactor neutronics and thermal hydraulics: Codes and calculations that have been benchmarked against the HEU reactor should be used to analyze the LEU reactor. The licensee should show that margins of safety are maintained in the LEU reactor. • Reactor accidents: The licensee should reanalyze the HEU Safety Analysis Report accidents using LEU fuel to determine the impacts from conversion. Particular concerns include changes in power per fuel element, fission product inventory, and reactivity. The licensee must also perform a review to determine whether conversion to LEU fuel introduces new acci- dent scenarios. Conversion should not have a significant impact on accident analysis results and normally should not introduce new accident scenarios. The application also identifies all necessary changes to the license, facil- ity, and operating procedures arising from conversion. The application must be limited to conversion and cannot include other changes or upgrades. Those are handled through the normal license amendment process. Once the USNRC reviews and accepts an application, it issues an en- forcement order directing the licensee to convert to LEU fuel and make any necessary changes to its license, facility, and procedures. By issuing enforce- ment orders, the USNRC assumes the burden for defending against any legal challenges that arise from conversion, thereby relieving the licensee from this responsibility. Several lessons have been learned from the civilian research reactor conversions that have been carried out to date in the United States. First, updating the safety analyses and preparing the conversion application take time and effort and can result in the discovery of other technical issues. Sec- ond, the key to successful conversions is to develop an LEU reactor design that can be successfully analyzed and built. Finally, conversion has benefits beyond the elimination of HEU: Most notably, it can result in increased technical expertise among reactor staff and improved knowledge of reactor characteristics and operating behavior. Conversion also provides valuable training opportunities: At university reactor facilities, many students have been involved in the development of conversion analyses. Russian Viewpoint on Regulatory Challenges V.S. Bezzubtsev The Russian Federation has been cooperating with the United States and the IAEA in several GTRI programs. These include the return of

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51 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION Russian-origin HEU fuel to the Russian Federation from countries in East- ern Europe and Asia; reduction of fuel enrichment in research and test reactors; and enhancement of physical security for high-risk radioactive sources. Active international cooperation and collaboration are necessary for achieving the strategic objectives of GTRI. ROSTEXNADZOR is the nuclear safety watchdog in the Russian Federation. It is responsible for regulating more than 6,000 facilities in the Russian Federation, including research and test reactors.18 It has three primary functions: regulatory control, licensing, and supervision of atomic energy facilities. The federal codes and standards developed by ROSTEXNADZOR are of two types: (1) general and (2) facility specific. The agency develops and promulgates federal codes and standards for atomic energy use, adminis- trative regulations, guidelines, and safety guides. The federal codes and standards provide general safety provisions for each type of atomic energy facility, for example, nuclear power plants, research reactors, icebreaker reactors, and nuclear fuel cycle facilities. These codes and standards also provide specific provisions for activities at these facilities including siting, construction, operation, and decommissioning. There are 10 separate codes and standards for research nuclear instal- lations, which include research reactors. These include, for example: • General Safety Assurance Provisions for Research Nuclear Instal- lations (NP-033-01) • Requirements for the Content of Research Nuclear Facility Safety Analysis Reports (NP-049-03) • Rules of Nuclear Safety for Research Reactors (NP-009-04) • Requirements for a Content of Action Plan for Protection of Person- nel in Case of an Accident at a Research Nuclear Installation (NP-075-06) Many of these codes and standards draw from IAEA documents, either in full or part, the latter being adapted to local conditions. An effort is currently under way to enhance the regulatory framework for nuclear and radiation safety at research reactors in the Russian Fed- eration. This includes the modification of current regulatory documents and the development of new regulations. The new regulations would re- quire periodic safety reviews of research reactors, development of rules for withdrawing research reactors from state supervision, and development of procedures for modifying the design, engineering, and operating documen- tation of research reactors. 18 This number includes radiation sources at hospitals.

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52 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS Federal Environmental, Industrial and Nuclear Supervision Service Status of О Nuclear Research Facilities 1991 2011 1991 2010 Н а No program 113 74 113 Фа Financial difficulties; ; Safety problems а П . 19 Э а 19 operating а а organizations ИР КС ПКС RRs CBs SCBs 32 30 12 31 Э аа Operation/ / а age > 30>30 yrs 11/5 24/17 28/12 Decommissioning 0 6 2 1 2 0 Under construction Figure 2-10.eps FIGURE 2-10 Status of research reactors in the Russian Federation. RR = research landscape reactors; CBs = critical assemblies; SCBs = subcritical assemblies. SOURCE: Bezzubtsev (2011). There were 74 licensed research reactors (including critical and subcriti- cal assemblies) in the Russian Federation in 2011. These are being operated by 19 organizations, including Rosatom and the Russian Academy of Sci- ences. These reactors comprise (Figure 2-10): • 32 research reactors (24 operating, 6 decommissioned, and 2 under construction) • 30 critical assemblies • 12 subcritical assemblies The average operation age of the research reactors is 24 years, but 17 reac- tors have been operating for more than 30 years. ROSTEXNADZOR is just beginning to develop regulations for the conversion of research reactors in the Russian Federation. The regulator does not see any serious barriers or obstacles that might prevent conver- sion-related licensing activities. The USNRC’s rich experience with fuel development and conversion-related approval activities would be useful for ROSTEXNADZOR in organizing its work.

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53 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION The specific issues that will need to be addressed by ROSTEXNADZOR in research reactor conversion in the Russian Federation are the following: • R&D for design and fabrication of new LEU fuel, LEU fuel tests, and validation of LEU fuel characteristics and operating conditions. • Safety demonstrations of fabrication, transportation, storage, and disposal of new LEU fuel. • Analysis of flux kinetics and distribution in reactor cores with LEU fuel. • Thermohydraulic analysis. • Safety analysis, including certification of computer codes; justifica- tion of safe operation limits and conditions; accident initiators; and modifi- cation of Safety Analysis Reports, plans of personnel and public protection, quality assurance programs, and operational procedures. • Modification of research nuclear installation designs. CHALLENGES POSED BY REACTORS THAT CANNOT BE CONVERTED Two presentations on the challenges posed by research reactors that cannot be converted were given by Panel 2.2 speakers: Jeffrey Chamberlin (U.S. Department of Energy, National Nuclear Security Administration) provided a U.S. viewpoint (Chamberlin, 2011), and G. Pshakin (Institute for Physics and Power Engineering in Obninsk) provided a Russian view- point (Zrodnikov et al., 2011). U.S. Viewpoint on Challenges Jeffrey Chamberlin GTRI is the key program within the U.S. government for implementing the U.S. policy to minimize the civilian use of HEU. GTRI’s mission is to reduce and protect vulnerable nuclear and radiological materials located at civilian sites worldwide. Its specific goals are to: (1) convert research reactors and isotope production facilities from HEU to LEU; (2) remove and dispose of excess nuclear and radiological materials; and (3) protect high-priority nuclear and radiological materials from theft and sabotage. GTRI’s Reactor Conversion Program is focused on converting civilian research reactors worldwide to operate on LEU fuel. Its goal is to convert or verify the shutdown of 200 civilian research reactors and HEU facilities by 2020.19 However, GTRI does not specifically encourage the shutdown of 19 This deadline slipped to 2022 while this report was being completed because of Fiscal Year 2011 federal budget reductions.

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54 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS research reactors; such decisions are made by facility operators. A research reactor does not have to be considered to be vulnerable to be a candidate for conversion. GTRI is focused on converting civilian reactors and HEU facili- ties that use HEU fuel because it provides for permanent threat reduction. Since the inception of GTRI in 2004, 23 HEU-fueled research reactors have been converted as part of the program, including 7 research reactors in the United States and 16 research reactors in other countries.20 The most recent conversions were the Kyoto University Research Reactor in Japan (March 2010) and the Rez Reactor in the Czech Republic (April 2011). As noted in Chapter 1, nearly all U.S. HEU-fueled reactors that can convert with existing LEU fuels have successfully been converted (see also Footnote 3 in this chapter). As noted in previous presentations, there are six HEU-fueled U.S. research reactors (ATR and its critical assembly, HFIR, MITR, MURR, and NBSR) that cannot be converted until a new LEU fuel is developed. Additionally, in December 2010, DOE and Rosatom signed an Implementing Agreement to perform feasibility studies for the possible conversion of six HEU-fueled research reactors in the Russian Federation. The reduction of HEU use in civilian applications is supported at the highest levels in the U.S. and Russian governments. In a joint statement issued on July 6, 2009, Russian Federation President Dmitry Medvedev and U.S. President Barack Obama issued a joint statement expressing their strong support for HEU minimization: We declare an intent to broaden and deepen long-term cooperation to further increase the level of security of nuclear facilities around the world, including through minimization of the use of highly enriched uranium in civilian applications and through consolidation and conversion of nuclear materials. This call for minimization was echoed in UN Security Council Joint Reso- lution 1887, which was issued in September 2009, and in the April 2010 Nuclear Security Summit. GTRI works in cooperation with reactor owners/operators to convert reactors to LEU fuel. This cooperation involves: • Performance of feasibility studies to determine if reactors can be converted and still achieve their missions without major changes in reactor structures or equipment. 20 In Chapter 1, it was noted that 35 conversions or shutdowns of HEU-fueled reactors have occurred since 2004. This larger number includes 10 reactors that were shut down and 2 reactors that were converted to LEU under domestic programs rather than GTRI.

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55 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION • Ensuring that required fuel assembly criteria for LEU conversion are satisfied; LEU fuel provides a similar service lifetime as the HEU fuel; there is no significant penalty in reactor performance; and safety criteria are satisfied. • Development of a schedule for conversion based on operational requirements, capabilities, and regulatory processes. • Demonstrating that conversion and subsequent reactor operations can be accomplished safely. • Determining, to the extent possible, that overall costs associated with conversion do not significantly increase the annual operating expen- ditures for reactor owners/operators. • Obtaining/verifying that agreements and authorities are in place to proceed with conversion. GTRI’s starting assumption for reactor conversions is that “anything is possible.” The experience gained from previous conversions demonstrates that there are many ways to overcome technical barriers. Indeed, many of the recent successful conversions of U.S. reactors were not thought to be possible 20-30 years ago. Although GTRI policy is to take all reasonable steps to convert facilities and reduce the use of HEU, there may be some facilities that are not feasible to convert. For example, a feasibility study for a particular reactor might indicate that conversion is not feasible because LEU fuel assembly criteria are not satisfied and a unique fuel development effort is not technically or economically feasible. This might be the case for fast reactors, fast critical assemblies, or HEU reactors with very small core volumes. In such cases, there are four options for addressing HEU minimization at such facilities: • Option 1: Assess the possibility of changing the facility mission such that it can be accomplished with LEU fuel. However, GTRI does not advocate a change of reactor mission for the sole purpose of converting. • Option 2: Reduce HEU enrichments. This may be technically fea- sible in some cases where LEU conversion is not. Note, however, that re- duced enrichments above 20 percent are not considered HEU minimization under international norms or GTRI policy. • Option 3: Shut down the facility or consolidate it with similar facilities if it is underutilized. • Option 4: If no other options exist for the facility other than to operate with HEU, remove all excess HEU and enhance physical protection measures to achieve threat reduction.

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56 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS GTRI considers each of these options to be “last resort” and does not en- dorse them as a matter of policy. These options must be considered on a case-by-case basis by the facility and the host government. Russian Viewpoint on Challenges G. Pshakin The BFS-1 and BFS-2 critical assemblies21 at the Institute for Physics and Power Engineering in Obninsk (Figure 2-11) provide a good example of reactors that cannot be converted to LEU fuel. These reactors, which are fueled with HEU and plutonium, were constructed in the late 1950s and early 1960s as part of the Soviet Union’s fast breeder program for nuclear energy development. Although these assemblies cannot be used for design- ing commercial-scale fast breeder reactors, they are useful for simulating fast breeder reactor cores, for fuel cycle research, and for studying the transmutation of minor actinides. This fuel used in these assemblies is not self-protecting22 and therefore poses special security concerns. Converting these facilities to LEU fuel cannot be accomplished without sacrificing the current mission. Moreover, even if the uranium enrichment of the fuel could be reduced, plutonium would still be required to simulate the cores of fast breeder reactors. There are two options for addressing the security concerns associated with these facilities: (1) shut down the facility and remove all nuclear ma- terials; or (2) organize a state-of-the-art materials protection, control and accounting (MPC&A) system and enhance the culture of personnel through proper training, motivation, and support. The second option is obviously preferable. The facility has cooperated with the United States to develop an MPC&A system. It includes a non-destructive analytical system based on high-resolution germanium detectors for isotopic measurement of ac- counted items; neutron coincident counters for nuclear material mass mea- surements; and specially designed access and monitoring systems. This program has to protect more than 100,000 HEU and plutonium discs that are used to model the cores of fast breeder reactors. 21 As noted in Chapter 1, a critical assembly contains sufficient fissionable and moderator material to sustain a fission chain reaction at a low (close to zero) level. It is designed so that fissionable and moderator materials can be easily rearranged in various geometries to mock up different reactor designs. 22 As noted in Chapter 1, a material is considered to be “self-protecting” if it produces a dose rate greater than 100 rad per hour at 1 meter in air. These high levels create substantial radiological barriers to illicit use.

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57 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION FIGURE 2-11 Photograph of a BFS critical assembly (BFS-1). SOURCE: Zrodnikov et al. (2011). Figure 2-11.eps bitmap DISCUSSION Time was set aside during this session for free discussion among sym- posium participants. Some of the key comments from that discussion are presented in this section. • Research reactors will continue to be an essential tool for many applications. B. Myasoedov commented that he expected the role of re- search reactors to grow in the future to support the development of more complex reactor designs for nuclear power plants, including those based on fast reactor designs; for radiopharmaceutical production; and for analytical methods (such a neutron activation analysis) to support safety monitoring and control. He suggested that Russia and the United States should agree to work together and with third-party countries to design a standardized research reactor that could be produced on an industrial basis. This would eliminate the need to design individual, customized cores and fuel elements. • Past experience suggests that successful conversion solutions can be found for most reactors. Jim Snelgrove commented that in view of the suc- cess that has occurred in converting reactors in the United States and some other countries, a key take-away message from this symposium should be that it is possible to find conversion solutions if one works hard enough to uncover them. Yu.S. Cherepnin added that some of the presentations in this session documented how enrichment levels could be reduced without degrading reactor performance. These examples should be publicized. H.-J. Roegler commented that conversion can result in improvements to reactors.

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58 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS • Current work under way in Russia on monolithic fuel development could pave the way for conversion of many Russian research reactors. Jim Matos commented that the densities of the LEU dispersion fuels described in the Russian presentations are too low to be used in converting many Russian reactors. Jim Snelgrove noted that monolithic pin-type LEU fuel is also being tested in Russia. This fuel is a potential replacement for the tube- type fuel that is now being used in Russian research reactors. The recent agreement between DOE and Rosatom to assess the feasibility of converting six Russian research reactors could play an important role in assessing the potential utility of this LEU fuel. • There may be some research reactors that cannot be converted. V. Ivanov noted that there may be some reactors with unique purposes that cannot be converted. For example, the multipurpose fast breeder reactor to be built in Dimitrovgrad will be fueled with HEU and plutonium. The concept of reducing risk by eliminating HEU does not make sense for this reactor because the HEU is used alongside plutonium. This is also true for critical assemblies. He also noted that the concept of “unique mission” has not yet been defined in Russia, and he suggested that there should be a limited list of parameters that could be applied to determine uniqueness. N.V. Arkhangelsky reminded symposium participants that it was recognized from the very beginning of the RERTR program that there are a number of research reactors that would not lend themselves to conversion, including fast breeders. • Reactor ageing is a potential complication for conversion, but it can be managed. V. Ivanov noted that unless national regulatory require- ments dictate conversion, the decision to convert, upgrade, or shut down a reactor will be made by the operator/owner. The owner/operator must determine whether it makes sense to convert the reactor if the remaining lifetime is negligible. H.-J. Roegler commented that, in his experience, re- search reactor ageing problems can be cured, although in some cases it can take time. A.N. Chebeskov commented that different reactor facilities may have access to different resources to manage ageing. Having a set of best practices to manage ageing could be a topic for international cooperation. • Reactor customers (users) are an important part of the conversion process. V. Ivanov commented that conversion work needs to be trans- parent to customers, not just designers and research reactor specialists. He suggested that it would make sense for the international community, including the customers of research reactors, to cooperate more closely on conversion. • There may be economic advantages to conversion. Richard Meserve noted that conversion may have economic advantages that were not dis- cussed by any of the symposium presenters. In particular, LEU costs could be lower, depending on how that material is priced, and costs for securing

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59 CHALLENGES AND OPPORTUNITIES ASSOCIATED WITH CONVERSION LEU fuel should be much lower than for HEU fuel. Jordi Roglans com- mented that transportation costs, especially international transportation costs, will be lower for LEU fuel because HEU is often transported by the military. • A worldwide ethic on conversion should be developed. Yu.S. Cherepnin suggested that the world community should develop a new ethic against operating reactors with HEU. Strong signals should be sent to operators of HEU reactors that they need to convert, and funding should be demanded from governments to support conversion. • Working together, the Russian Federation and the United States have played and will continue to play important global roles in research reactor conversion. N. Laverov noted that the Russian Federation has decommissioned 200 nuclear submarines and, working with the United States, has returned 100,000 tonnes of natural uranium and 500 tonnes of HEU from foreign countries. The recent agreement between DOE and Rosatom to assess the feasibility of converting six Russian research reac- tors is an important step for eliminating HEU use in Russian research reactors. It is important that the Russian Federation and the United States serve as an example to countries by reducing the enrichments of their research reactors to lower levels. REFERENCES Adams, A. 2011. Regulatory Challenges and Solutions: High-Enriched to Low-Enriched Ura- nium Fuel Conversion. Presentation to the Research Reactor Conversion Symposium. June 9. Bezzubtsev, V. 2011. Regulating Safe Operation of Russian Research Reactors. Presentation to the Research Reactor Conversion Symposium. June 9. Chamberlin, J. 2011. Challenges Posed by Research Reactors That Cannot be Converted (U.S. Viewpoint). Presentation to the Research Reactor Conversion Symposium. June 9. Cherepnin, Yu. 2011. Experience of Resolving the Problems Arising in Conversion of Research Reactors. Presentation to the Research Reactor Conversion Symposium. June 9. IAEA [International Atomic Energy Agency]. 1995. Management of Research Reactor Ageing. IAEA-TECDOC-792. Vienna: International Atomic Energy Agency. Roegler, H. 2011. Obsolescence & Ageing: Findings from the IAEA Initiative on Research Reactor Ageing and Ageing Management. Presentation to the Research Reactor Conver- sion Symposium. June 9. Roglans, J. 2011. Maintaining Performance and Missions (U.S. viewpoint). Presentation to the Research Reactor Conversion Symposium. June 8. Ryazantsev, E. 2011. Ageing and Obsolescence of Research Reactors. Presentation to the Research Reactor Conversion Symposium. June 9. Stevens, J. 2011. Core Modifications to Address Technical Challenges of Conversion. Presenta- tion to the Research Reactor Conversion Symposium. June 8. Svyatkin, M.N., Izhutov, A.L., and Petelin, A.L. 2011. Use of Research Reactors of Scientific Centre RIAR. Presentation to the Research Reactor Conversion Symposium. June 8. Tetiyakov, I.T. 2011. Modification of the Reactor Cores. Presentation to the Research Reactor Conversion Symposium. June 8.

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60 CONVERTING U.S. AND RUSSIAN RESEARCH REACTORS Wachs, D. 2011. Research and Test Reactor Fuel System Development. Presentation to the Research Reactor Conversion Symposium. June 8. Zrodnikov, A., Pshakin, G., and Matveenko, I. 2011. Research Reactors That Cannot be Converted. Presentation to the Research Reactor Conversion Symposium. June 9.